This invention relates to a system for exposing X-ray film automatically to X-rays, to an adequate density, and more particularly, to an arrangement for detecting X-rays in the system.
Generally, in a system for exposing an object with X-rays, it is required to expose an X-ray film, to an appropriate density, with X-rays transmitted through the object. Therefore, an X-ray diagnosis apparatus is provided with means for exposing the X-ray film with X-rays, automatically to an appropriate density. In this automatic X-ray exposure means, the X-rays transmitted through an object are detected, and when the detected value, i.e., the total quantity of X-rays, reaches a predetermined value, exposure of the object to X-rays is stopped, whereby adequate exposure of the X-ray film is obtained. In such an automatic X-ray exposure system, an intensifying screen, for converting the X-rays into light rays, is located between the object and X-ray film, and a light-transmission device for transmitting the resultant light rays to a light detector, i.e., a photoelectron multiplier (hereinafter referred to as a multiplier) is provided between the light detector and an area in which X-rays, i.e., light rays, are to be picked up (i.e., a light-pickup field).
As the light-transmission device, a light transmission plate made of acrylic resin is used. Light rays incident on the acrylic resin plate and transmitted through this plate by random reflection, are detected by the photo-multiplier. When the integral of the detected signal reaches a predetermined value, it is determined that the X-ray film has been adequately exposed, and exposure is stopped.
When using the acrylic resin plate as the light-transmission device, the following problems arise:
With the acrylic resin plate, the light transmissivity is not so satisfactory. Therefore, random reflection of light rays on the surface of the acrylic resin plate is utilized for light transmission. For this reason, the light-transmission efficiency is inferior. This means that it is necessary to position the photomultiplier in the vicinity of the acrylic resin plate. The thickness of the detector as a whole is thus increased, which constitutes a significant drawback when assembling the detector in an X-ray diagnosis apparatus. Furthermore, usually, the greater the distance to the photo-detector, the greater the attenuation of the light signals. Therefore, various contrivances are required for obtaining uniform detection efficiency in the light-pickup field.